Improved instrument for aligning fixing screws to be inserted in transverse holes of nails for long bones, in particular medullary nails

ABSTRACT

The invention relates to an improved-structure instrument (1) for allowing the alignment of fixing screws (2) to be inserted in transverse holes (3, 13) of nails (4) for long bones, in particular medullary nails, of the type comprising an arched arm (15) having a free distal end (6) connectable to a proximal end (16) of a head (7) of the nail (4) in which the transverse holes (3, 13) are formed, and a proximal handle portion (5), as well as a connection portion (20) between the distal end (6) and the proximal handle portion (5). Advantageously, the connection portion (2) comprises at least one through-hole (23, 33) for receiving a guide tube (10) for a drilling bit, the through-hole (22, 33) having an axis coinciding with the axis of one of the transverse holes (3, 13,) and manually operated quick-locking means (25) are associated with the through-hole (23, 33) so as to lock in a stable position the corresponding tube (10) inserted in the instrument (1).

The present invention relates to an improved-structure instrument forallowing the alignment of fixing screws to be inserted in transverseholes of nails for long bones, in particular medullary nails.

The invention relates in particular, but not exclusively, to aninstrument comprising an arched arm having a free distal end connectableto a proximal end of the nail, and a proximal handle portion, as well asa connection portion between the distal end and the proximal handleportion.

FIELD OF APPLICATION

In the technical sector of the present invention it is known to use longnails which are inserted in the medullary cavity of long bones, such asthe femur, the tibia or the humerus, in order to mend fractures whichhave occurred along a section of the long bone or in the trochantericportion of a femur.

These nails are provided with transverse through-holes intended toreceive bone screws which reach the through-hole penetrating through thecortex of the bone until they reach the medullary nail. Thethrough-holes are not necessarily perpendicular to the main axis of thenail, but may be inclined with respect to this axis depending on theirposition in the nail or the type of use.

In order to form holes in the bone which may be aligned perfectly withthe transverse holes in the medullary nails, usually instruments areused to guide the bone drilling bits so that they are coaxial with thetransverse through-holes provided in the medullary nail.

PRIOR ART

An instrument of this type is described for example in U.S. Pat. No.5,334,192 or in the US patent application No. 2003/220651.

This instrument has an essentially arch-shaped arm with a distal endwhich is connected to the proximal end of a medullary nail inserted in along bone, for example a femur, and a proximal handle end provided withthrough-holes for receiving at least one guide tube.

The through-holes of the handle are oriented so as to be aligned withthe transverse holes in the medullary nail, so that a drill bit may beinserted into the hole guide tube so as to perforate under the skin thecortex of the long bone and emerge precisely opposite the inlet of atransverse through-hole.

The handle may be provided with a plurality of through-holes which alsohave respective axes interfering with each other so as to allowalignment with different transverse through-holes in the medullary nail.

When a guide tube is inserted in one of the aforementioned through-holesof the handle, it must be locked so that it is held stably in position.

Locking in position of the tubes is required by orthopaedic surgeons soas to prevent them from falling in the operating theatre during use andthus becoming no longer sterile.

Moreover, the tubes must be kept axially in a fixed position where thefree end is situated adjacent to the bone so as to ensure a precisemeasurement of the length of the bone screws necessary for theoperation, by means of the special instrument.

In some embodiments described for example in the aforementioned patenttexts, the handle of the instrument contains a core which is axiallyslidable and which, upon operation by the user, is able to interferewith the tube portion which passes through the handle so as to fasten itin that position.

However, these embodiments are not particularly convenient and easy tooperate manually while the surgical operation is being performed.

In other embodiments a handle is provided with elastically deformableportions which allow the guide tube to be locked in position; however,these solutions have also not proved to be particularly reliable duringuse.

For instance another known solution is disclosed in the U.S. Pat. No.6,039,739 disclosing an instrument for allowing the alignment of fixingscrews to be inserted in transverse holes of nails for long bones, inparticular medullary nails, of the type comprising an arched arm havinga free distal end connectable to a proximal end of a nail head whereinsaid transverse holes are formed at a handle proximal portion, as wellas a connection portion between the distal end and the proximal handleportion. The connection portion comprises at least one through-hole forreceiving a guide tube for a drilling bit and locking means areassociated to said at least one through-hole so as to lock in a stableposition the corresponding tube inserted in the instrument.

Those locking means include a flexible second part of the handle thathas a free end and is extended in a cantilever manner in parallel to themain part of the handle; when this second part is flexed by hand itinterferes with the main part of the handle thus gripping the guidetube.

This gripping action is however not so stable and does not allow to freethe surgeon hand for other handling necessities.

The technical problem forming the basis of the present invention is thatof devising an improved instrument for the alignment of bone screws tobe inserted in transverse nail holes for long bones, which hasstructural and functional characteristics such as to allow locking inposition of the guide tubes inserted in the instrument handle whileovercoming the drawbacks mentioned with reference to the prior art.

Another objet of the invention is that of making it possible to achievelocking in position of the guide tubes by means of a simple manualmovement, including that of a finger of a hand which is already employedgripping the instrument.

Another object of the invention is to devise an instrument of theaforementioned type which has a simple constructional design and iscomposed of a minimum number of component parts.

A further object of the invention is that of providing an instrument ofthe aforementioned type where the guide tube may also be removed withthe same ease at the end of the operation.

SUMMARY OF THE INVENTION

The proposed solution forming the basis of the present invention is thatof housing the tubes in through-holes formed in the central body of theinstrument and equipping these holes with a manually operatedquick-locking mechanism which allows the corresponding tube to be lockedin position once its correct position has been defined.

Based on this proposed solution the technical problem is solved by animproved-structure instrument for allowing the alignment of fixingscrews to be inserted in transverse holes of nails for long bones, inparticular medullary nails, of the type comprising an arched arm havinga free distal end connectable to a proximal end of a head of the nail inwhich said transverse holes are formed, and a proximal handle portion,as well as a connection portion between the distal end and the proximalhandle portion, characterized in that said connection portion comprisesat least one through-hole for receiving a guide tube for a drilling bit,said at least one through-hole having an axis coinciding with the axisof one of said transverse holes; manually operated quick-locking meansbeing associated with said at least one through-hole so as to lock in astable position the corresponding tube inserted in the instrument;wherein

-   -   at least a chamber is formed inside the body of said connection        portion around said through-hole for housing said locking means;    -   at least a lateral opening in communication with said chamber;    -   a two components quick-locking cam assembly forming said locking        means: a first component being integral with said body of said        connection portion around said guide tube and the other        component including a cam and being angularly movable with        respect to the first component;        -   a trigger element of said other component projecting from            said lateral opening to be manually operated thus moving the            first component with said cam interfering with said guide            tube.

In mode details, the through-holes in the connection portion of theinstrument are at least two in number and each of them has an axiscoinciding with the axis of a corresponding transverse hole.

Moreover, the quick-locking means comprising a cam locking assemblyhoused in a chamber formed around a corresponding through-hole areprovided for each of said through-holes.

The housing chamber has opposite openings that make it laterallyaccessible for said central body; the locking means which comprise apair of components each provided with a corresponding through-hole forsaid tube are housed inside the chamber; one component being integralwith the central body of the instrument and the other component beingangularly movable with respect to the previous component so as to lockin position the tube by means of interference between the correspondingholes.

The corresponding holes of the two components are slightly axiallyoffset with respect to each other. Moreover, one of said correspondingholes has a flat portion protruding along a chord of the circular shapeof the hole in the manner of a cam.

The movable component is a butterfly member with a cylindrical body anda pair of opposite operating lugs integrally formed and laterallyprojecting from the central body of the instrument through saidopenings.

Moreover, at least one of the lugs is shaped with at least one concavesurface which can be engaged by a finger of the hand of the orthopaedicsurgeon so as to angularly rotate said butterfly member of thequick-locking assembly inside the respective housing chamber.

The cylindrical body is housed completely inside one of the chambers andis capable of rotating with limited angular travel until one of the twolugs comes into abutment against an edge of the openings.

Instead, the fixed component which cooperates with said butterfly memberis essentially a sleeve inserted with limited play inside thecylindrical body and provided with a pin projecting perpendicularly fromits inner wall for engaging with a guide slot formed in a bottom wall ofsaid cylindrical body.

The characteristic features and advantages of the instrument accordingto the invention will emerge from the description, provided hereinbelow,of a non-limiting example of embodiment thereof with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective and schematic view of the instrument providedaccording to the present invention for the alignment of fixing screws tobe inserted in transverse holes of nails for long bones, in particularmedullary nails;

FIG. 2 shows a schematic, vertical, side-elevation view of theinstrument according to the invention;

FIG. 3 shows a perspective and schematic view of a detail of theinstrument according to the invention;

FIG. 4 shows a schematic cross-sectioned side view of the instrumentaccording to FIG. 1;

FIGS. 5 and 6 show respective schematic front views of the detail ofFIG. 3 in two different operating conditions;

FIG. 7 shows a side view of a fixing screw intended to be inserted in atransverse hole of a medullary nail;

FIG. 8 shows a view from above of the head of the screw according toFIG. 7;

FIG. 9 shows a perspective yew of a tool used with the instrumentaccording to the present invention for installation of the screwsaccording to FIG. 7;

FIG. 10 shows a side view of a pair of components of the tool accordingto FIG. 9;

FIG. 11 shows a perspective view of a detail of the tool according toFIG. 9 at the moment where it engages with the head of the screwaccording to FIG. 7;

FIG. 12 shows a schematic view of a detail of the end of the toolaccording to FIG. 9;

DETAILED DESCRIPTION

With reference to these figures, 1 denotes overall and in schematic forman instrument designed according to the present invention with animproved structure for allowing the alignment of fixing screws 2 to beinserted into transverse holes 3, 13 of a nail 4 for long bones, inparticular a medullary nail.

Medullary nails are long nails intended to be inserted into themedullary cavity of long bones, such as the femur, the tibia or thehumerus, in order to mend fractures which have occurred along at least asection of the long bone or in the trochanteric portion of a femur.

The nail 4 shown in the figures is intended, however, for use withpaediatrics patients and/or adolescents and has dimensions compatiblewith this type of application. However, the principles of the presentinvention are applicable to any type of medullary nail without thisresulting in any limitation of the rights of the Applicant.

More particularly, the nail 4 comprises a proximal head 7 and a stem 8extending in the distal direction. The head 7 has an associatedlongitudinal axis of extension, while the stem 8 has a longitudinal axisinclined with respect to the axis of the head 7 of the nail.

The head 7 has, formed therein, at least two holes 3 and 13 transverseto its longitudinal axis.

The holes 3 and 13 are through-holes and are intended to receive fixingscrews 2 (shown in FIG. 7) which reach the corresponding hole,penetrating through the cortex of the bone. The through-holes 3 and 13are not necessarily perpendicular to the axis of the head 7, but may beinclined with respect to this axis and with respect to each other.

In order to form holes in the bone which may be directed towards and bealigned perfectly with the transverse holes 3, 13 of the head 7,drilling bits (not shown since conventional) are used and are guided bytubes 10 removably mounted on the instrument 1. The tubes 10 will bereferred to below as pointers or guide tubes.

The instrument 1 according to the present invention has a generalstructure substantially in the form of an arched arm 15 with a distalend 6 which is free and can be connected to a proximal end 16 of thenail 4 and an opposite proximal handle portion 5.

The handle 5 is intended to be gripped by the orthopaedic surgeon inorder to insert and position correctly the nail 4, which is connected atthe distal end of the instrument, inside the medullary cavity of thebone involved in the operation.

The free distal end 6 of the instrument 1 is situated at one end of aslightly arched distal portion 15 provided with engaging means 18 forengaging and fastening the proximal end 16 of the head 7 of the nail 4to the distal end 6 of the instrument 1.

Advantageously, according to the present invention, the instrument 1comprises a connection portion 20 between said distal portion 15 and thehandle 5. The connection portion 20 does not have substantially anyinterruption in continuity with the handle 5 and may be formed as onepiece therewith. However, for the purposes of the present invention, theconnection portion 20 is to be regarded as separate from the handle andcould also be mounted removably on the said handle 5.

This connection portion 20 forms the central body of the instrument 1and is the portion which has, formed therein, through-holes 23 and 33intended to receive the guide tubes 10 for the drilling bits. In oneembodiment it is possible to envisage also a single hole in theconnection portion 20 of the instrument.

Each of the holes 23 and 33 has a respective axis A-A and B-B, clearlyvisible in FIG. 2, which is aligned and coincides with the axis of arespective transverse hole 3 and 13 in the head 7 of the nail 4.

Essentially, the axes A-A and B-B are coaxial with the axes of thetransverse holes 3, 13 in the nail 4 so as to guide the bone drillingbits until they reach the transverse holes 3 and 13.

Still according to the present invention, the tubes 10 are supported inthe central body 20 of the instrument 1 by means of the through-holes 23and 33.

More particularly, locking means 25 are provided for stably locking thetubes 10 in position inside the respective through-holes 23 and 33.

Inside the body 20, in the central position of each through-hole 23 and33, a respective chamber 24, 34 for housing the locking means 25 isprovided. Each chamber 24, 34 is substantially a square seat havingopposite openings 17 and 27 which make it laterally accessible for thecentral body 20. The aforementioned locking means 25 are provided insideeach of these chambers.

Each chamber 24 or 34 houses inside it with limited axial play theaforementioned locking means 25 which comprise a quick-locking camassembly formed by means of two components: one component 39 integralwith the central body 20 of the instrument and one component 9 angularlymovable with respect to the component integral with the body 20.

More particularly, the quick-locking assembly is manually operated andcomprises a trigger comprising a first butterfly member 9 with a maincylindrical body 29 and a second coupling member 39 inserted inside thecylindrical body 29. The coupling member 39 is rigidly connected to thecentral body 20 of the instrument 1.

The butterfly member 9 of the trigger component has a pair of oppositewings 11, 19 or operating lugs formed integrally with the cylindricalbody 29 and laterally projecting from the central body 20 of theinstrument 1 through the openings 17 and 27.

Each of the lugs 11, 19 is shaped with at least one concave surface 28which can be engaged by a finger of the hand of the orthopaedic surgeonso as to manually operate the locking means 25, angularly displacing thebutterfly member 9 of the quick-locking assembly inside the respectivehousing chamber 24, 34.

The cylindrical body 29 is housed entirely inside one of the chambers24, 34 and is able to rotate with limited angular travel until one ofthe two lugs 11 or 19 comes into abutment against an edge of theopenings 17 or 27, when no tube is inserted.

The cylindrical body 29 has a bottom wall 26 provided with a hole 22through which the tube 10 passes when the butterfly member is housedinside the respective chamber 24, 34.

The hole 22 has a flat portion 21 protruding essentially along a chord22 of the circular shape of the hole 22 so as to form a cam.

The diameter of the hole 22 is slightly greater than the outer diameterof the tube 10.

A curved slot 36 is also provided in the bottom wall 26 of thecylindrical body 29 in a predefined spaced relationship with respect tothe hole 22 and concentric with it along a short section.

The coupling member 39 which cooperates with the butterfly member 9 isessentially a sleeve inserted with limited play inside the cylindricalbody 29 and provided centrally with a hole 32, Advantageously, the hole32 is slightly axially offset with respect to the hole 22 of thecylindrical body 29. The eccentricity e between the axis A-A of the hole22 and the axis B-B of the hole 32 is shown schematically in FIG. 3 andconsists of a few millimetres.

The diameter of the hole 32 corresponds substantially to the outerdiameter of the tube 10.

A pin 37 projects perpendicularly from the inner wall of the sleeve 39so as to be inserted inside the slot 36 and be guided inside this slot36 along a predefined angular travel path equal to the extension of thesaid slot. The pin 37 passes through a hole 38 formed in turn inside thesleeve 39.

The sleeve 39 also has a hole 40 for the insertion of a presser 41 whichperforms the function of a friction shoe and which allows the sleeve 39to be fastened to the housing chamber 24 or 34 so that the sleeve 39 isrigidly connected together with the central body 20 of the instrument 1.

More particularly, the hole 40 is threaded and is intended for insertionof the presser 41 which has the function of eliminating undesirablemovements of the butterfly member 9 when the mechanism is not closed soas to lock a tube in position. In this way it is avoided that the userhas to deal with freely rotating components when the instrument is beingassembled and prepared and when the butterfly member 9 of the trigger isstill in the “open” position.

At the same time, the pin 37 which rigidly fixes the member 39 to thebody 9 passes inside the hole 38 of the sleeve 39 and therefore insidethe slot 36 of the butterfly member 9.

Essentially, only the butterfly member 9, with the lugs 11, 10projecting from the openings 17 and 27, is rotationally movable withfriction and with limited angular travel inside the associated housingchamber 24 or 24 formed in the central body of the instrument 1.

This butterfly member 9 of the quick-locking cam assembly cooperateswith the sleeve-like coupling member 39 so as to allow quick locking inposition of the corresponding guide tube.

As can be clearly seen in FIGS. 5 and 6, in the open position the twoholes 32 and 22 of the respective components 39 and 29 of the camlocking assembly are substantially axially offset as a result of theeccentricity e, and thus a relative rotation of the components 39 and 20causes a constriction of the guide tube 10 inserted inside the holes 22and 32 by means of the flat cam portion 21 and stable locking inposition of the said tube.

In other words, the guide tube 10 may be inserted without difficultyinside one of the housing holes 23 or 33 provided in the centralconnection body 20 of the instrument via the holes 22 and 32 of thelocking assembly.

Once the tube 10 is correctly seated, the orthopaedic surgeon may decideto lock the tube 10 easily and rapidly in the closing position once ithas been ensured that the same has its end situated next to the skin,and then the bone, of the patient so as to allow a tissue-protectionfunction to be performed during incision and drilling of the bone untilone of the transverse holes 3 or 13 of the head 7 of the nail alreadyinserted inside the medullary cavity of the bone is reached.

By means of a simple manual action on one or other of the lugs 11, 19the surgeon is able to displace angularly the butterfly member 9 of thequick-locking cam assembly and position it in the configuration shown inFIG. 6 where the flat portion 21 of the hole 22 interferes with thediameter of the hole 32 and locks the tube 10 by means of interferencein the desired position.

In this connection particular attention is drawn to the relativedisplacement of the guide slot 36 with respect to the pin 37 of thecoupling member integral with the instrument 1.

Once the hole has been formed in the bone owing to guiding of a drillingbit by means of the tube 10, a fixing screw 2 must be introduced so asto engage with one of the transverse holes 3 or 13 in the head 7 of thenail 4.

In order to grip, insert and engage in a distal position a screw 2inside the corresponding hole 3, 13 of the nail 4, it is envisagedusing, according to the present invention, a tool 50 shown in FIG. 7.

This tool 50 may be equipped with a screwdriver having an operativedistal end 51 and a proximal handle end 52.

The tool 50 extends along its longitudinal axis and may comprise a shank53 removably engaged with the handle 52. Obviously it is quite possiblefor the shank to be fastened beforehand to the handle without thislimiting in any way the rights of the Applicant. The screw 2 which isinserted inside the transverse holes of the head 7 of the nail 4 has ahead 12 shaped to allow a form-fit with the distal end 51 of the tool50.

For this purpose the head 12 has a peripheral crown 44 formed by analternation of protuberances 45 and recesses 46 which are regularlyspaced relative to each other.

The head 12 has centrally a recess 48 which is in turn shaped in themanner of a plurality of lobes 43 which correspond, in terms of numberand position, to the lobes and the protuberances 45 of the recess in thescrew.

In the preferred example of embodiment described here by way of anon-limiting example, the crown 44 has an alternating arrangement of sixprotuberances and six recesses, but it is quite possible to provide adifferent number and arrangement thereof. This corresponds to a centralrecess 48 with a hexalobular form.

Advantageously, the distal end 51 of the tool 50 is configured so as tobe able to engage with the head 12 of the screw 2 both on the outsidethereof and on the inside thereof in the central recess 48.

As shown in FIG. 10, the shank 53 of the tool 50 comprises two maincomponents, an outer component 60 and an inner component 62. A thirdtubular component 66 rigidly connected to a proximal ring 67 cooperateswith the outer component 60 so as to rotate it manually with respect tothe inner component 62.

The outer component 60 is a tubular rod with distal end 61 intended tosurround the crown 44 of the head 12 of the screw 2 and engage with itby means of a matching form 71. The proximal end 64 of the tubular rod60 is connected to the third component which is a proximal tubularelement 66 with a larger diameter, provided with a pin 65 or a presserprojecting inwards. The tubular element is rigidly connected to theouter ring 67.

The inner component 62 is a core with a distal end 67 which is taperedand has a cross-section shaped with the same form as the central recess48 of the screw 2. The proximal end 68 of the core 62 is threaded so asto be able be screwed onto the handle 52 of the tool 50.

At a predefined distance from this threaded proximal end 68 there is anannular stop element 69 intended to form an end-of-travel stop for theaxial sliding movement of the tubular element 66 when the core 62 isinserted concealingly inside the tubular rod 60.

A spring is optionally provided, being inserted between the annular stopelement 69 and the threaded proximal end 68 so as to keep the instrumentin position when it is in the closed and open positions.

The core 62 is also provided with a slit 70 extending along a shortlongitudinal section in a distal position with respect to the annularstop element 69 and intended to receive the pin 65 or a presser formedon the tubular element 66 so as to form an axial sliding guide for thispin 65.

When the core 62 is mounted coaxially inside the tubular rod 60 of thetool 50 a small relative axial movement of the two components 60 and 62is possible, this allowing the respective distal ends 61 and 67 to beradially aligned and to engage with a form-fit with the head 12 of thescrew 2.

In fact, the inner form of the distal end 61 of the tubular rod 60engages with the perimetral crown 44 of the screw 2, while the shapeddistal end 67 of the core 62 engages by means of a form-fit with thecentral recess 48 of the same screw 2.

Essentially, it is as though the tool 50 had a distal end 51 comprisingan outer component 61 intended for a form-fit with the head 12 of saidscrew 2 and an inner component 67 intended for a simultaneous form-fitwith the central recess 48 of said screw 2.

Moreover, the aforementioned outer distal end 61 and inner distal end 67are axially slidable relative to each other following the slidingmovement of the core 62 inside the tubular rod 60 on the guide of thepin 65 inside the slit 70.

In this way, the retention of the screw 2 at the distal end 51 of thetool 50 is ensured by a double form-fit.

Moreover, the inner form-fit, namely that of the distal end 67 of thecore 62 also allows the screw 2 to be rotationally operated, beingsubstantially a form-fit which also allows a twisting moment to betransferred.

In this way, not only is stable gripping of the screw 2 ensured at thedistal end 51 of the tool 50, but it is also possible to screw orunscrew the screw into/from the corresponding seat formed by thetransverse hole in the head 7 of the nail 4 without adversely affectingin any way the aseptic condition of the components used.

From the above description it is clear that the instrument 1 and theassociated tool 50 according to the present invention may be used incombination as parts of a single operating kit.

The tool 50 offers the great advantage that it has a simple and low-costconstructional design, ensuring stable retention of the heads of thebone screws during the delicate phase when they are inserted intotransverse through-holes of the medullary cavity and also easy removalthereof during explantation.

1.-15. (canceled)
 16. An improved-structure instrument for allowing thealignment of fixing screws to be inserted in transverse holes of nailsfor long bones, in particular medullary nails, of the type comprising:an arched arm having a free distal end connectable to a proximal end ofa head of the nail in which said transverse holes are formed, and aproximal handle portion as well as a connection portion between thedistal end and the proximal handle portion, at least one through-hole insaid connection portion for receiving a guide tube for a drilling bit,said at least one through-hole having an axis coinciding with the axisof one of said transverse holes; locking means associated with said atleast one through-hole so as to lock in a stable position thecorresponding tube inserted in the instrument; wherein at least achamber is formed inside the body of said connection portion around saidthrough-hole for housing said locking means; at least a lateral openingin communication with said chamber; a two components quick-locking camassembly forming said locking means: a first component being integralwith said body and placed around said guide tube and the other componentincluding a cam and being angularly movable with respect to the firstcomponent; said other component being provided with a first hole throughwhich the tube passes; said first component being provided with a secondhole through which the tube passes; the first and second holes areslightly axially offset; said first hole having a flat portionprotruding essentially along a chord of the circular shape of the firsthole so as to form said cam; a trigger element of said other componentprojecting from said lateral opening to be manually operated thus movingthe other component with said cam interfering with said guide tube, arelative rotation of the components causes a constriction of the guidetube inserted into the holes by means of the flat portion and stablelocking in position of the said guide tube.
 17. The instrument accordingto claim 16, wherein said through-holes in the connection portion of theinstrument are at least two in number and each of them has an axiscoinciding with the axis of a corresponding transverse hole.
 18. Theinstrument according to claim 17, wherein locking means comprising aquick-locking cam assembly housed in a chamber formed around acorresponding through-hole are provided for each of said through-holes.19. The instrument according to claim 18, wherein each of said chambershas opposite openings that make it laterally accessible for said centralbody; said locking means being housed in the chamber and comprising apair of components each provided with a corresponding through-hole forsaid tube; one component being integral with the central body of theinstrument and the other component being angularly movable with respectto the previous component so as to lock in position the tube by means ofinterference between the corresponding holes.
 20. The instrumentaccording to claim 19, wherein the movable component is a butterflymember with a cylindrical body and a pair of opposite operating lugsintegrally formed and laterally projecting from the central body of theinstrument through said openings.
 21. The instrument according to claim20, wherein at least one of the lugs is shaped with at least one concavesurface which can be engaged by a finger of a hand of the orthopaedicsurgeon so as to angularly rotate said butterfly member of thequick-locking assembly inside the respective housing chamber.
 22. Theinstrument according to claim 20, wherein said cylindrical body ishoused completely within one of the chambers and is capable of rotatingwith limited angular travel until one of the two lugs comes intoabutment against an edge of the openings in the absence of the guidetube.
 23. The instrument according to claim 20, wherein the fixedcomponent which cooperates with said butterfly member is essentially asleeve inserted with limited play inside the cylindrical body andprovided with a pin perpendicularly projecting from its inner wall forengaging with a guide slot formed in a bottom wall of said cylindricalbody.
 24. The instrument according to claim 16, including fixing screwsto be inserted in transverse holes of nails wherein at least one of saidfixing screws comprises a head shaped as a crown with a central recessfor a form-fit with the distal end of a tool for retaining the screw.25. The instrument according to claim 24, wherein said head shaped as acrown has an alternation of regularly spaced protuberances and recesses.26. The instrument according to claim 24, wherein said central recess isshaped in the manner of a plurality of lobes which correspond to saidprotuberances in terms of number and positioning.
 27. The instrumentaccording to claim 24, wherein it comprises a tool having at least onedistal end comprising an outermost end intended for a form-fit with thehead of said screw and an inner end intended for a simultaneous form-fitwith the central recess of said screw.
 28. The instrument according toclaim 12, wherein said outer end and inner end are axially slidablerelative to each other.